Membrane biofilm reactor for removing contaminants from ground water

ABSTRACT

Apparatus and methods for water treatment are described, particularly for the simultaneous removal of nitrate, perchlorate, and other organic contaminates from contaminated water using a membrane biofilm reactor (MBfR).

PRIORITY

The present application claims priority to U.S. Provisional ApplicationSer. No. 60/920,993, filed on Mar. 30, 2007 which is hereby incorporatedby reference in its entirety.

TECHNOLOGICAL FIELD

The invention is in the field of water treatment, particularly in theremoval of nitrate, perchlorate, and other organic contaminates fromcontaminated water using a membrane biofilm reactor (MBfR).

BACKGROUND Membrane Biofilm Reactor (MBfR)

Biological denitrification is relatively inexpensive and the final wasteproduct is innocuous nitrogen gas. Perchlorate reduction can beperformed using the same or different organisms, and the final wasteproduct is chloride. While well-studied for waste-water treatment, thereis relatively little information available regarding the use ofbiological denitrification and perchlorate reduction for producingdrinking water.

Biological denitrification and perchlorate reduction are typicallyperformed on a biofilm formed in a membrane biofilm reactor (MBfR)device, which provide a large surface area for the biofilm and means forcontacting the biofilm with liquid and/or gas nutrients and electrondonors. MBfR devices support the growth of slow-growing bacteria, suchas autotrophs, and are particularly efficient in removing contaminantspresent at low concentrations, and in removing contaminants to nearlyundetectable levels, as required for drinking water applications.

Where the levels of electron donors present in the ground-water are toolow to support complete biological denitrification or perchloratereduction, an organic electron donor (in the case of heterotrophicdenitrification) or an inorganic donor (in the case of autotrophicdenitrification) can be added to MBfR device for utilization by thebiofilm. In the cases of biological denitrification and perchloratereduction, the electron donor is often hydrogen gas (H₂), which issupplied to the biomass via hollow membranes upon which the biofilmforms.

While, biological denitrification and perchlorate reduction have bothbeen performed in MBfR devices, the different redox potentials of theseoxidized contaminants, as well as other oxidized contaminants that maybe present in the ground water, has heretofore resulted in thesequential oxidation of contaminants based on their redox potential,often resulting in residual levels of toxic compounds with comparativelylow redox potentials. Such effluent water is unsuitable for use asdrinking water without further treatment to reduce the levels of theseresidual contaminants.

The need exists for more efficient apparatus and methods for removingoxidized contaminants from ground water using MBfR technology,preferably apparatus and methods capable of simultaneous reduction of avariety of contaminants using a single MBfR device.

REFERENCES

-   Rittmann, B. E. (1995) J. Hrubek. 5B:61-67.-   Xu, J. et al. (2003) Environ. Eng. Sci. 20:405-22.-   Liessens, J. et al. (1993) J. AWWA 85:144-54.-   Green, M. (1995) Applied Microbiology and Biotechnology 43: 188-93.-   Urbain, V. et al. (1996) J. AWWA 88:75-86.-   Lazarova, V. Z. et al. (1992) Water Science Technology 26:555-66.-   Soares, M. I. M. and Abeliovich, A. (1998) Wat. Res. 32:3790-94.-   Rittmann, B. E. and McCarty, P. L. (2001) Environmental    Biotechnology: Principles and Applications. McGraw-Hill Book Co.,    New York.-   Banaczak, J. E. et al. (1999) J. Radioanalytical and Nuclear    Chemistry 241:385-435.-   Lee, K. C. and Rittmann, B. E. (2000) Water Sci. Technol. 41:219-26.-   Lee, K. C. and Rittmann, B. E. (2002) Wat. Res. 36:2040-52.-   Kurt, M. et al. (1987) Biotechnology and Bioengineering 29:493-501.-   Dries, D. et al. (1988) Water Supply 6:181-92.-   Nerenberg, R. et al. (2002) J. AWWA 94:103-14.-   Adham, S. et al. (2004) Membrane BioFilm Reactor Process for Nitrate    and Perchlorate Removal in AWWA Research Foundation Report.-   Ergas, S. J. and Ruess A. F. (2001) J. Wat. Suppl. Res &    Technol.-AQUA 50:161-71.-   Nerenberg, R. (2003) Perchlorate removal from drinking water with a    hydrogen-based, hollow-fiber membrane biofilm reactor. Ph.D.    Dissertation at Northwestern University-   Loach, P. A. and Fasman, G. D. (Eds.) (1976) Handbook of    Biochemistry and Molecular Biology (3^(rd) ed.), Physical and    Chemical Data, Vol. I, pp. 123-30, CRC Press.-   CRC Handbook of Chemistry and Physics 1st Student Edition, CRC    Press, Boca Raton, Fla., USA, 1988.

SUMMARY

The following aspects and embodiments thereof described and illustratedbelow are meant to be exemplary and illustrative, not limiting in scope.

In one aspect, a method for reducing the concentration of oxidizedcontaminants present in ground water is provided, comprising:

(a) providing an source of contaminated ground water comprising nitrateand perchorate to an MBfR device;

(b) operating the MBfR device in a recycle mode using the contaminatedground water for a first period of time sufficient to form a biofilm inthe MBfR device for performing denitrification in the influent water;and

(c) operating the MBfR device in a feed mode using the contaminatedwater to produce denitrified effluent water;

wherein the denitrified effluent water further comprises reduced levelsof perchlorate compared to the influent water.

In some embodiments, the influent water further comprisestrichloroethylene (TCE), and the denitrified effluent water furthercomprises reduced levels of TCE compared to the influent water.

In some embodiments, a chloride material balance calculation isperformed to account for the chloride derived from the reduced TCE.

In some embodiments, the influent water further comprisesnitroso-dimethyl-amine (NDMA), and the denitrified effluent waterfurther comprises reduced levels of NDMA compared to the influent water.

In some embodiments, the levels of nitrate are substantiallyundetectable in recycle mode prior to switching to feed mode.

In some embodiments, the method further comprises:

(d) operating the MBfR device in a recycle mode using influent watercomprising at least a portion of effluent water from (c) for a secondperiod of time sufficient to acclimate the biofilm to reduceperchlorate; and

(e) operating the MBfR device in a feed mode using influent watercomprising at least a portion of effluent water from (c) to reduce thelevels of perchlorate in the influent water.

In some embodiments, the influent water further comprisestrichloroethylene (TCE), and the effluent water from (e) furthercomprises reduced levels of TCE compared to the influent water of (a).

In some embodiments, a chloride material balance calculation isperformed to account for the chloride derived from the reduced TCE.

In some embodiments, the effluent water further comprisesnitroso-dimethyl-amine (NDMA), and the effluent water from (e) furthercomprises reduced levels of NDMA compared to the influent water of (a).

In some embodiments, the method further comprises:

(f) applying the effluent water from (e) to a second MBfR device havinga biofilm acclimated to perchlorate reduction; and

(g) operating the second MBfR device in a feed mode using as influentwater the effluent water from (e) to produce effluent water from thesecond MBfR device having further reduced levels of perchlorate comparedto the effluent water from the MBfR device of (a).

In some embodiments, the levels of perchlorate after (g) aresubstantially undetectable.

In some embodiments, denitrification and perchlorate reduction areperformed by autotrophic bacteria using hydrogen gas as an electrondonor.

In some embodiments, the autotrophic bacteria are indigenous to theground water.

In some embodiments, the ability of the biofilm to performdenitrification in (b) is determined by comparing the concentration ofnitrate in the recirculating water in the MBfR effluent water to theconcentration of nitrate in the influent water.

In some embodiments, the MBfR device comprises polyester hollowfilaments for supporting the biofilm.

In a related aspect, a method for reducing the concentration ofcontaminants in ground water is provided, comprising:

(a) providing a source of contaminated ground water comprising nitrate,perchorate, and trichloroethylene (TCE) and/or nitroso-dimethyl-amine(NDMA) to an MBfR device;

(b) operating the MBfR, device in a recycle mode using the contaminatedground water for a first period of time sufficient to form a biofilm inthe MBfR device for performing denitrification in the influent water,wherein the ability of the biofilm to perform denitrification isdetermined by comparing the concentration of nitrate in the water in therecycle mode of the MBfR to the concentration of nitrate in the influentwater; and

(c) operating the MBfR device in a feed mode using the contaminatedground water to produce effluent water reduced in nitrate, perchorate,and TCE and/or NDMA;

wherein the levels of nitrate, perchorate, and TCE and/or NDMA arereduced simultaneously.

In some embodiments, the autotrophic bacteria are indigenous to theground water.

In some embodiments, a chloride material balance calculation isperformed to account for the chloride derived from the reduced TCE.

In some embodiments, the autotrophic denitrifying and perchloratereducing bacteria are the same type of bacteria, which are acclimated todenitrifying and/or perchlorate reduction by operating the MBfR in arecycle mode using ground water from which nitrate and/or perchlorate isto be removed.

In some embodiments, the autotrophic denitrifying and perchloratereducing bacteria are different types of bacteria, which can be selectedto form a biofilm for denitrifying and/or perchlorate reduction byoperating the MBfR in a recycle mode using water from which nitrateand/or perchlorate is to be removed.

In another aspect, drinking water is provided, which is produced bysimultaneously reducing nitrate and perchlorate contaminants in groundwater using an MBfR device adapted to support a biofilm comprisingautotrophic denitrifying and perchlorate reducing bacteria.

In some embodiments, simultaneously reducing nitrate and perchloratecontaminants in an MBfR device further includes simultaneously reducingtrichloroethylene (TCE).

In some embodiments, a chloride material balance calculation isperformed to account for the chloride derived from the reduced TCE.

In some embodiments, simultaneously reducing nitrate and perchloratecontaminants in an MBfR device further includes simultaneously reducingnitroso-dimethyl-amine (NDMA).

In some embodiments, simultaneously reducing nitrate and perchloratecontaminants is performed in a single MBfR device, or a plurality orMBfR devices in fluid communication with a common source of influentwater.

In some embodiments, the MBfR or plurality of MBfRs comprise polyesterhollow filaments for supporting the biofilm.

In addition to the exemplary aspects and embodiments described above,further aspects and embodiments will become apparent by reference to thedrawings and by study of the following descriptions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a hollow membrane filament in an MBfR device.

FIG. 2 illustrated the bench-scale MBfR apparatus used in experiments.

DETAILED DESCRIPTION I. Definitions

Prior to describing aspects and embodiments of the present apparatus andmethods, the following terms are defined for clarity. Terms andabbreviations not defined should be accorded their ordinary meaning asused in the art. Note also that singular articles, such as “a” and “an”encompass the plural, unless otherwise specified or apparent fromcontext.

As used herein, the terms “biofilm” or “biomass” refer collectively tomicroorganisms that grow on the exterior surface of hollow filaments inan MBfR. Such organisms typically affect removal of one or morecontaminants present in influent liquid entering the MBfR. A biofilm mayinclude a single type of microorganism or a plurality of different(types of) microorganisms, which may be indigenous to the ground waterbeing treated or inoculated into the ground water or the MBfR device. Abiofilm may be a single layer of microorganisms or a plurality of layersof microorganisms. Bacteria are the preferred microorganisms. Oneskilled in the art will appreciate that biofilms accumulates in an MBfRduring set-up and operation but are not a “component” of an MBfR deviceor system, e.g., as provided to an end user.

As used herein, the term “biofouling” refers to the process by which abiofilm/biomass clogs, blocks, or otherwise restricts fluid and/or gasflow in an MBfR apparatus to the point of adversely affecting theoperation of the apparatus.

As used herein, “acclimating” a biofilm to reduce a particularcontaminant, or chemical class of contaminants, refers to exposing thebiofilm to influent water that includes preselected levels of theparticular contaminant(s) and, optionally other contaminants to (i)select for microorganisms capable of reducing the particularcontaminant, (ii) induce the expression of enzymes in a microorganismcapable of reducing the particular contaminant, or (iii) a combinationthereof. Acclimation may be accomplished in a feed mode by continuing topass the influent water comprising the preselected levels of theparticular contaminant(s) through the MBfR device until the biofilm isacclimated, or by cycling (recirculating) such influent water throughthe MBfR device, until the biofilm is acclimated.

As used herein, the terms “inerts” and “inert materials” refercollectively to debris and other material that accumulates in the lumenof the hollow fibers. Such debris and material includes but is notlimited to particulate matter present in the gas introduced into thelumen of hollow fibers, liquid and solutes that diffuse into the lumenfrom the exterior surfaces of the hollow fibers, organisms that grow inthe lumen of the hollow fibers, and dust.

As used herein, the term “interleaf” or “interleaf material” refers to aporous, substantially planer material used to separate and maintain thespacing of the hollow filaments. An exemplary material is an open meshmade from recyclable plastic.

As used herein, the term “warp fiber” refers broadly to inert fibers(i.e., fibers not required to support a biomass) that can be combinedwith hollow filaments to separate and maintain the spacing of the hollowfilaments. The warp fibers may be uniformly spaced along the length ofthe hollow filaments, and may be under sufficient tension to limit themovement of the hollow fibers, which assists in maintaining spacing.Exemplary warp fibers are made from recyclable plastic.

As used herein, a “substantially undetectable” level of a particularcontaminant refers to either (i) a level below which the contaminantcannot be detected using a technology approved for water testing, (ii) anumerical concentration as described herein, or (iii) a maximum levelestablished by a regulatory body. Numerical concentrations are less thanabout 0.2 N-mg/L for nitrate; less than about 0.5 μg/L for perchlorate;less than about 0.5 μg/L for TCE; and less than about 2 ng/L for NDMA.Different definitions may apply to different embodiments, and any one ormore of these definitions may be specified by appropriate language orexcluded, as in the case of a proviso.

As used herein, “simultaneous” reduction or removal of an oxidizedcontaminant occurs when a first oxidized contaminant with lower redoxpotential is reduced by a biofilm, while a substantial amount of asecond oxidized contaminant with a higher redox potential remains in thewater. A substantial amount is 20%, 30%, 40%, 50%, or more.

As used herein, “treating” ground water refers to decontaminating, orreducing the levels of a contaminant, in the ground water.

As used herein, “drinking water” refers to water suitable for humanand/or animal consumption.

As used herein, “oxidized contaminants” are compounds present in groundwater that can be reduced by microorganisms to produce partially orfully reduced compounds, preferably having reduced toxicity orreactivity compared to the original oxidized compounds. Exemplaryoxidized contaminants are nitrate, nitrite, perchlorate, chlorate, andthe like.

As used herein, “different types of microorganisms” are differentgenera, species, strains, or other genetic variation of a microorganismsuch as bacteria.

II. Introduction

The present apparatus and methods relate to the removal of oxidizedcontaminants from ground water using an MBfR device and method. Inparticular, the apparatus and methods involve treatment of ground waterin an MBfR device to reduce nitrate and perchlorate, as well as otheroxidized contaminants such as trichloroethylene (TCE) andnitroso-dimethyl-amine (NDMA), to relatively harmless compounds.

An aspect of the apparatus and methods is that contaminants havingdifferent redox potentials can be reduced simultaneously. This featureis unexpected, since contaminants with different redox potentials wouldbe expected to be sequentially reduced, beginning with those with thehighest redox potential and ending with those with the lowest redoxpotential.

Another aspect of the apparatus and methods is that a single MBfR devicecan be used for both nitrate and perchlorate reduction, as well as NDMA,and TCE reduction. The reduction of these contaminants may occursimultaneously or sequentially in a single MBfR device, or in aplurality of MBfR device in communication with common influent source.Where the reduction of the different species occurs sequentially, thebiofilm can be allowed to acclimate to contaminants with different redoxpotentials during the course of decontaminating a batch of influentwater. However, the biofilm need not be stripped from the MBfR and a newbiofilm reestablished for reduction of a different group of oxidizedcontaminants.

A further aspect of the apparatus and methods is the use of a chloridematerial balance calculation to account for the chloride derived fromreduced compounds. This ensures that volatile contaminants are reducedto harmless compounds released in effluent water, as opposed to beinglost to the atmosphere due to evaporation. This aspect of the apparatusand methods is particularly important with the respect to TCE, which mayevaporate from an influent water reservoir prior to reduction in theMBfR device, giving the appearance of destroying the contaminant whileactually venting the contaminant to the atmosphere.

In experiments performed in support of the present apparatus andmethods, contaminated influent water samples were obtained from theAerojet Site in Rancho Cordova (Sacramento, Calif., USA). Particularwells at the Aerojet Site have inordinately high concentrations ofnitrate, perchlorate, TCE, and NMDA, and ground water from such wellswas used to evaluate the performance of the present apparatus andmethods.

III. Experiments Performed in Support of the Invention

The following experiments were performed to illustrate features of thepresent apparatus and methods.

A. Contaminated Water from the Aerojet GET E/F Facility

Water originating from the Aerojet GET E/F Treatment Facility(Sacramento, Calif., USA) contaminated with perchlorate and TCE atlevels of 1,600 μg/L and 580 μg/L, respectively, was used in a firsttest of the MBfR device detailed in Example 1. The MBfR device wasoperated in a recycle (i.e., 100% recirculation) mode for two days toallow the growth and acclimation of a biofilm in the influent water.After this initial recycling period, the nitrate concentration in therecirculating contaminated water was reduced to less than 0.2 N-mg/L(Table 1), which levels is considered “undetectable.” Nitratecontaminants were presumed to be first reduced by the biofilm.

Following the initial period of operation in a recycle mode, the MBfRwas operated in a feed mode at a rate of 0.2 to 0.3 mls/minute freshcontaminated influent water. After six days of operation in feed mode, afirst effluent water sample was collected and provided to Aerojet foranalysis. A second effluent sample was collected following 14 days ofoperation in the feed mode, and also submitted to Aerojet. The levels ofvarious contaminants in the influent and effluent water are summarizedin Table 1.

TABLE 1 Summary of Results using GET E/F water Mode Recycle Hydrogen(Recirc/ Flow Rate Flow rate Pressure Time NO₃ ¹ TCE² Perchlorate² NDMA²Sample # Feed) (ml/min) ml/min (psig) (Days) (mg/L) (μg/L) (μg/L) (μg/L)GET E/F 0 0 0 0 0 10 580 1,600 0.071 GET E/F Recirc 200 0 4-5 2 <0.2 NANA NA GET E/F Feed 200 0.2-0.3 4-5 6 <0.2 5 190 0.044 GET E/F Feed 2000.2-0.3 4-5 14 <0.2 1.2 <4 0.0048 ¹Analysis conducted by Applied ProcessTechnology ²Analyis conducted by Aerojet

While the biofilm was monitored only for nitrate reduction while theMBfR was in the recycle mode, it is apparent from the data presented inthe Table 1 that perchlorate, TCE, and NDMA were all at least partiallyreduced in the effluent water (compared to the influent water) when theMBfR device was operated in the feed mode. These results are the firstto show the simultaneous reduction of nitrate, perchlorate, TCE, andNDMA present in ground water. The results were unexpected based on theredox potentials of the various contaminants, based on which one wouldexpect the complete reduction of nitrate prior to the complete reductionof perchlorate. TCE has the lowest redox potential and should presumablynot be reduced until all contaminants with higher redox potentials arereduced (Loach, P. A. and Fasman, G. D. (Eds.) (1976) Handbook ofBiochemistry and Molecular Biology (3rd ed.), Physical and ChemicalData, Vol. I, CRC Press. pp. 123-30). However, TCE appeared to bereduced while the levels of other contaminants, such as perchlorate,were still detectable.

B. Contaminated Water from Well 3673 (First Sample)

To further evaluate the ability of the test MBfR device tosimultaneously remove different contaminants present in ground water, asecond sample of water was received from Well 3673 at the Aerojet site.Well 3673 has particularly high concentrations of TCE (32,000 μg/L) andperchlorate (28,000 μg/L).

As above, the MBfR was first operated in a recycle mode until thenitrate levels were non-detectable, and then operated in a feed modeusing fresh influent water from Well 3673. Following three days ofoperation in a recycle mode, the nitrate concentration wasnon-detectable (i.e., less than 0.2 N-mg/L). After feeding fresh waterfrom Well 3763 for 10 days, effluent samples were taken and analyzed forTCE and perchlorate (Table 2). A second effluent sample was taken after29 days and a final effluent sample was taken after 38 days.

As shown in Table 2, the concentrations of both TCE and perchlorate inthe effluent water appeared to decrease, suggesting simultaneousreduction of contaminants having different redox potentials. However,analysis of the influent water for TCE on day 38 indicated that that theTCE concentration had been fallen, e.g., by evaporation or by some othermechanism. While the perchlorate concentration in the influent water onday 38 was not analyzed, perchlorate would not be expected to evaporateor degrade as in the case of TCE.

Despite the evaporation of TCE from the influent water applied to theMBfR device, a significant amount of TCE was also reduced by thebiofilm. Based on the data in Table 2, a period of time of from about 29to about 38 days appears to be required to acclimate the microorganismsin the biofilm for metabolism of TCE and perchlorate, and or allow thegrowth of organisms capable of metabolizing TCE and perchlorate.

TABLE 2 Summary of Results using water from well 3673 Mode RecycleHydrogen (Recirc/ Flow Rate Flow rate Pressure Time NO₃ ¹ TCE²Perchlorate² Sample # Feed) (ml/min) ml/min (psig) (Days) (N-mg/L)(μg/L) (μg/L) Well 3670 0 0 0 0 0 12 32,000 28,000 Well 3670 Recirc 2000 4-5 3 <0.2 NA NA Well 3670 Feed 200 0.2-0.3 4-5 10 <0.2 33 17,000 Well3670 Feed 200 0.2-0.3 4-5 29 <0.2 21 150 Well 3670 Feed 200 0.2-0.3 4-538 <0.2 6.8³ 400 ¹Analysis conducted by Applied Process Technology²Analyis conducted by Aerojet ³Influent TCE concentration analysed andfound to be 52 μg/L

C. Contaminated Water from Well 3673 (Second Sample)

Following the successful reduction of high concentrations of perchlorateand TCE in the water from Well 3673, a second sample of thiscontaminated water was provided for testing. To reduce the evaporationof TCE, the sample reservoir was changed from plastic to glass andsealed with aluminum foil.

To account for the contaminants present in the influent water in theanalysis of the effluent water, total chloride levels were measured inthe effluent water and compared to total chloride levels in the influentwater, thereby allowing the calculation of chloride material balance. Inthis manner, the chloride present in the effluent water could attributedto either the reduction of perchlorate or the reduction of TCE. Inaddition, the levels of contaminants present in the influent water(particularly TCE) were monitored over the course of the test to accountfor losses due to evaporation or other mechanisms. A summary of theresults from this second test using water from Well 3673 is presented inTable 3.

TABLE 3 Summary of results using water from well 3673 (second run) Days12 24 30 Influent Effleunt Influent Effleunt Influent Effleunt Sample ID(122105-0) (122105-12) (122105-0B) (122105-24) (122105-0C) (122105-30)Inorganics (mg/L)¹ Perchlorate 28 0.61 29 0.075 23 0.072 F 0.091 0.10.086 0.098 0.1 0.093 Cl 8.6 21 8.9 20 8.5 20 NO₂ ND <0.05 0.37 NR 0.58<0.05 Br <0.10 <0.1 <0.10 0.1 0.11 0.11 NO₃ 13 <0.1 12 <0.1 11 <0.1 PO₄0.49 <0.30 0.45 0.31 0.51 <0.30 SO₄ 9.9 9.6 10 7.5 9.9 7.5 Organic(μg/L)¹ TCE 15,000 170 6,600 330 3100 160 1,1-DCEe 82 2.0 51 4.2 <10<0.5 1,2-DCEe 36 4.4 30 7.5 <10 0.52 CH₂Cl₂ 290 <0.5 <0.5 <0.5 <10 <0.5CHCl₃ ND 1.8 12 3.3 <10 <0.5 1,1-DCEa ND 0.74 3 0.73 <10 <0.5 1,2-DCEaND 1.5 5.6 2.5 <10 <0.5 ¹All analysis conduct by Aerojet

As shown in Table 3, the concentration of TCE and other chlorinatedsolvents in influent water decreased over time. The initial TCEconcentration in the influent to the MBfR was 15,000 μg/L and after 30days had fallen to 3,100 μg/L. Nonetheless, as above, a significantreduction in the concentration of the TCE and other chlorinated solventsoccurred in the MBfR device. Interestingly, no increase in theconcentrations of 1,2-dichloroethylene (1,2-DCE) or vinyl chloride wereobserved from the reduction of the TCE, as previously reported. Thechloride concentration of all effluent samples increased from about 8.5mg/L to about 20 mg/L, which was consistent with perchlorate and TCEreduction.

A more detailed analysis of the chloride levels in the influent water,in which chloride material balance was determined by calculating thechloride concentration resulting from perchlorate and TCE reduction tochloride, is summarized in Table 4. The sum of the amount of chlorideproduced from the reduction of perchlorate and TCE, plus the chlorideinitially present in the water, should correspond to the amount ofchloride present in the effluent water.

TABLE 4 Chloride material balance Days 12 24 30 Chloride fromperchlorate (mg/L) 9.77 10.32 8.18 Chloride from TCE (mg/L) 13.22 5.592.62 Total Chloride from perchlorate and 22.99 15.91 10.80 TCE (mg/L)Chloride in MBfR Infleunt (mg/L) 8.6 8.9 8.5 Calculated Chloride (mg/L)31.59 24.81 19.30 Chloride in MBfR Effleunt (mg/L) 21 20 20 ChlorideMaterial Balance 66.5% 80.6% 103.6%

As shown in Table 4, after 12 days of MBfR operation, the chlorideconcentration in the influent water resulting from perchlorate reductionwas calculated to be 9.77 mg/L, while the chloride concentration in theeffluent water resulting from TCE reduction was calculated to be 13.22mg/L. The total chloride concentration in the influent water was 31.59mg/L. The total chloride concentration in the MBfR effluent water on day12 was 21 mg/L, thus the chloride in the effluent water accounted foronly 66.5% of the expected amount of chloride. However, the chloridebalance was 103.6% at day 30, suggesting that all the chloride producedby the reduction of the perchlorate and TCE was ultimately accounted forby the chloride material balance calculation.

D. Summary of Results

The results described above indicate that an MBfR device and method canbe used to reduce nitrate, perchlorate, NDMA, and TCE in contaminatedground water. The MBfR device was even effective in removing thesecontaminants from influent water from Well 3673, which has particularlyhigh levels of perchlorate and TCE contamination. Measuring the chloridematerial balance in influent and effluent water confirmed the reductionof both perchlorate and TCE to chloride; nonetheless, the resultssuggest that TCE loss to evaporation should be considered in testing anddesigning water treatment devices and methods to avoid the excessiveloss of such contaminants to the atmosphere prior to reducing them toless harmful compounds. 1,2-DCE and vinyl chloride were not detected,suggesting that TCE is not broken down into these compounds aspreviously suggested.

While the reduction in nitrate, perchlorate, TCE, and NDMA wassubstantial in all tests, the levels of perchlorate and TCE were notreduced to non-detectable levels, presumably because these compound havea lower redox potential than other contaminants present in the influentwater (e.g., nitrates). A non-detectable level for perchlorate is lessthan about 4 μg/L and a non-detectable level for TCE is less than about0.5 μg/L. Thus, while simultaneous reduction of nitrate, perchlorate,and other oxidized contaminants was observed, the complete reduction ofperchlorate and TCE may require two MBfR devices operating in series,wherein the first MBfR device reduces the concentration of perchlorateand TCE by about 95%, and the second MBfR device further reduces theconcentrations of perchlorate and TCE to non-detectable levels.

As discussed, a period of time is required to allow a biofilm to developfrom indigenous microorganisms in an MBfR device. In the tests performedabove, the MBfR was operated in a recycle mode during this period oftime to allow microorganisms to acclimate to the nutrient conditionsand/or grow to sufficient density to allow operation of the MBfR devicein a feed mode. The acclimation time required to achieve completenitrate reduction was only about two to about three days. Theacclimation time for perchlorate reduction was about 24 days. Theacclimation time for TCE reduction appears to be about 30 to about 38days. However, while such times represent the acclimation periods foroptimal contaminant reduction, nitrate, perchlorate, TCE, and NDMA wereall reduced simultaneously, at least to some extent, followingacclimation of the MBfR device for nitrate reduction.

Notably, some sulfate appeared to have been reduced, presumably tosulfide, although the odor of hydrogen sulfide was not apparent in theeffluent water from the MBfR device. Since the redox potential ofsulfate is even lower than the redox potential of perchlorate, thisobservation further supports the simultaneous reduction of contaminantshaving different redox potentials, rather than the sequential reductionof contaminants in order of redox potential.

These results of the above-described experiments demonstrate thatreduction of nitrate, perchlorate, TCE, and NDMA are not mutuallyexclusive and all these contaminants can be reduced simultaneously in asingle MBfR device. This result is surprising since conventional wisdomholds that the oxidized contaminant species with the highest redoxpotential should be completely reduced before there is significantreduction of contaminant species with lower redox potentials.

IV. Contaminants and Microorganisms

A. Contaminants

The present apparatus and methods have largely been exemplified forreduction of particular oxidized contaminants present in ground water,such as nitrate, perchlorate, TCE, and NDMA, although they can be usedto reduce a variety of oxidized contaminants present in ground water.

Trichloroethylene (TCE) is a sweet-smelling, colorless, non-flammableliquid with the formula empirical formula C₂HCl₃ and the followingstructure:

TCE is used to degrease metals, as an extraction solvent for oils andwaxes, in dry cleaning, as a refrigerant, and as a fumigant. TCE wasoriginally used as an anaesthetic and an analgesic in obstetrics untilits carcinogenic and mutagenic properties were recognized. Uponingestion, TCE is readily decomposed into toxic compounds such as1,2-dichloroacetylene and trichloroacetic acid. The State of California(USA) has set a maximum permissible level for TCE in drinking water of 5ppb.

N-nitrosodimethylamine (NDMA) is a carcinogenic, mutagenic, andteratogenic disinfection by-product of chloramine treatment The State ofCalifornia (USA) has set a maximum permissible level of NDMA in drinkingwater of 10 ng/L. NDMA is an odorless, yellow, oily volatile liquid withthe empirical formula C₂H₆N₂O and the following structure:

Other oxidized contaminants that can be removed instead of, or inaddition to, the exemplified contaminants include, but are not limitedto, nitrite, chlorate, bromate, halongenated organic contaminants, otherN-nitrosamines, inorganic oxyanions such as selenate, chromate, andarsenate, organic solvents and pesticides, such as tetrachloroethylene(PCE), trans 1,2-dichloroethylene (trans-DCE), dichloromethane (DCM),chloroform (CF); nonylphenol (NP), triclosan (TCS), Bisphenol-A (BPA),and estradiol equivalents (EEQ).

B. Microorganisms

The apparatus and methods have also been exemplified using bacteriaindigenous to the waste water being treated. Typically, a plurality ofdifferent types of bacteria is present in the influent water, althoughthe present methods contemplate the use of a single type of bacteria. Insome cases, the same bacteria may reduce nitrate and perchlorate. Inother cases, different bacteria may reduce nitrate and perchlorate.

The types of bacteria present in a biofilm may change over time. Forexample the population may include predominantly denitrifying bacteriawhen nitrate concentrations are high and may include predominantlyperchlorate reducing bacteria when nitrate concentrations are low. Thecomposition of a biofilm may be intentionally changed, e.g., byrecirculating water having particular known levels of a nitrate,perchlorate, other preselected contaminants to acclimate the biofilm toreducing a particular contaminant species.

The use of bacteria indigenous to the ground water has the advantagethat such bacteria are already adapted to the available nutrients.However, where the ground water is essentially sterile, where indigenousbacteria fail to acclimate to the MBfR environment, where a largeinitial inoculum of bacteria into an MBfR device is desired, or wheremore precise control of the types and amounts of bacteria present in abiofilm is desired, one or more types of micoorganisms can be introduced(i.e., inoculated) into the influent water and/or MBfR device. Examplesof such micoorganisms are described, below.

Autotrophic Denitrification Systems

Autotrophic denitrification and perchlorate reduction using hydrogen asan electron donor has been described. Hydrogen gas (H₂) is capable ofreleasing a pair of electrons per mole, enabling the full reduction ofnitrate and perchlorate according to the following equations:

H₂→2H⁺+2e ⁻  (1)

2.5H₂+NO₃ ⁻→0.5N₂+2H₂O+OH⁻  (2)

2H₂+ClO₄ ⁻→Cl⁻+O₂+2H₂O  (3)

The reduction of nitrate and perchlorate are believed to proceed asfollows:

NO₃ ⁻→NO₂ ⁻→NO⁻→N₂O⁻→N₂+O₂  (4)

ClO₄ ⁻→ClO₃ ⁻→ClO₂ ⁻→Cl⁻+O₂  (5)

Redox potential for each of these reactions can be found in anappropriate reference manual, such as the CRC Handbook of Chemistry andPhysics, published by CRC Press, Boca Raton, Fla., USA and the Handbookof Biochemistry and Molecular Biology (3^(rd) ed.), Physical andChemical Data, Vol. I, CRC Press.

Hydrogen-oxidizing bacteria include both hydrogen-oxidizing, autotrophicbacteria and bacteria able to utilize organic carbon and other energysources in addition to hydrogen. Hydrogen-oxidizing bacteria arepreferred in some embodiments of the present apparatus, systems, andmethods. In the presence of oxidized contaminants, such bacteria reducean oxidized form of a primary electron acceptor in a sufficient amountto sustain a viable, steady-state biomass within the aqueouswater-treatment system. Deriving energy for growth via reduction isreferred to as a dissimilatory reduction. Examples of hydrogen-oxidizingbacteria include but are not limited to Pseudomonas pseudoflava,Alcaligenes eutrophus, Alcaligenes paradoxus, Paracoccus denitrificans,and Ralstonia eutropha, which can all used nitrate, and a Dechloromonasstrain, which can use perchlorate.

The use of hydrogen gas an electron donor has several major advantages,for example, (i) H₂ is the least expensive donor per equivalent ofelectrons supplied, (ii) H₂ is non-toxic to humans, (iii) H₂ is evolvedfrom water open to the surface, thereby eliminating residue that couldcause biological instability or disinfection byproducts in drinkingwater, and (iv) H₂ supports the growth of autotrophic bacteria, which donot need an organic carbon source.

Autotrophic denitrification of NDMA using H₂ as an electron source isbelieved to proceed through a three-step reduction with the final wasteproducts being ammonia and dimethylamine.

Heterotrophic Degradation of Nitrate and Perchlorate

Heterotrophic processes for nitrate and perchlorate reduction have usedethanol, acetate, or methanol as an electron-donor supplement (Liessens,J. et al. (1993) J. AWWA 85:144-54; Green, M. (1995) AppliedMicrobiology and Biotechnology 43: 188-93; Urbain, V. et al. (1996) J.AWWA 88:75-86). Ethanol and methanol are alcohols that are federallyregulated, and methanol has acute health risks. Acetate, wheat straw,and corn syrup have been used but may leave donor residuals in thetreated water due to overdosing or fluctuations in the influent nitrateconcentration. Such residuals encourage organism growth in downstreamdistribution systems, causing numerous problems, including increasedplate counts, unpleasant taste and odor, accelerated corrosion, anddecreased flow capacity. As a result, water treatment systems utilizingheterotrophic donors typically require post-treatment to producebiologically stable water.

Removal of nitrogenous contaminants is usually performed by denitrifyingbacteria or “nitrifiers”, which include two major groups of aerobic,chemolithoautotrophic bacteria. Ammonia-oxidizing bacteria oxidizeammonia to nitrite, and nitrite-oxidizing bacteria (NOB) oxidize nitriteto nitrate. The first process is performed by a number of facultativeanaerobes commonly found in soil. The second process, sometimes referredto as “true” denitrification, is performed by a more select group ofbacteria exemplified by Paracoccus denitrificans, Alcaligenes eutrophus,Alcaligenes paradoxus, Pseudomonas pseudoflava, Vibrio dechloraticansCuznesove B-1168, Acinetobacter thermotoleranticus, Ideonelladechloratans, GR-1 (a strain identified to belong to theβ-Proteobacteria, Paracoccus denitrificans, Wolinella succinogenes, andRalstonia eutropha. Pseudomonas pseudoflava, Alcaligenes eutrophus,Alcaligenes paradoxus, Paracoccus denitrificans, and Ralstonia eutrophacan all use hydrogen gas as an electron donor. Ralstonia eutropha is apreferred bacteria available from the American Type Culture Collection(ATCC; Manassas, Va., USA) as collection number 17697.

Perchlorate-reducing bacteria are generally facultative anaerobes ormicroaerobes. The bacteria use acetate, propionate, isobutyrate,butyrate, valerate, malate, fumerate, lactate, chlorate, and oxygen aselectron donors but typically not methanol, catechol, glycerol, citrate,glucose, hydrogen, sulfate, selenate, fumerate, malate, Mn(IV), orFe(II). Most perchlorate-reducing bacteria are Proteobacteria.Dechloromonas, Dechlorosoma, and strain GR-1 are β-Proteobacteria, whileAzospirillum is an α-Proteobacteria. Strains of Dechloromonas andDechlorosoma can use lactate as an electron donor, and strains ofDechlorosoma can use ethanol as an electron donor. With the exception ofthree Dechloromonas strains, all perchlorate-reducing bacteria can usenitrate as an electron acceptor.

Despite its drawbacks, the true yield (Y) of denitrification, expressedas grams dry weight (DW) per gram oxygen demand (OD) of electron donor,is significantly higher in heterotrophic denitrification than inautotrophic denitrification. For example, the yield for heterotrophicdenitrification utilizing acetate is 0.225 g DW/g OD donor, while theyield for autotrophic denitrification utilizing H₂ is 0.107 g DW/g ODdonor. An advantage of higher yield is faster growth and, consequently,shorter startup times. A disadvantage of higher growth is that thebiomass must be partially wasted from the system by backwashing or gassparging, or by maintaining sufficient flow velocity or turbulence inthe reactor to prevent the overgrowth of the biomass, which leads toclogging and poor flow characteristics.

With respect to other oxidized contaminants, autotrophic denitrificationof NDMA believed to proceed through a three-step reduction with thefinal waste products being ammonia and dimethylamine. Autotrophicdenitrification of TCE is believed to yield 1,2-DCE and vinyl chloride,although the results described herein suggest than different reducedproducts may be produced. TCE is also reduced by iron-reducing bacteriaand sulfate-reducing bacteria, which are found in soil.

V. Materials for Use in MBfR Devices

A. Membrane Materials

One type of membrane for use in the present MBfR device and method ishollow-filament membrane, as described for use in denitrification(Ergas, S. J. and Ruess, A. F. (2001) J. Wat. Suppl. Res & Technol.-AQUA50:161-71), perchlorate reduction (Nerenberg, R. (2003) Ph.D.Dissertation at Northwestern University), and TCE reduction to ethaneand chloride. Using such membranes, H₂ gas is diffused through the wallsof a the hollow filaments, which are sufficiently porous to allow thediffusion of H₂ gas through the walls of the filaments, while beingsufficiently non-porous so as to allow the use of long continuousfilaments, while ensuring sufficient H₂ pressure in the distal end ofthe hollow filaments.

The illustration in FIG. 1 shown a hollow filament containing a 1-μmthick nonporous, hydrophobic polyurethane layer sandwiched bymicro-porous polyethylene walls. The dense polyurethane layer allowsslightly pressurized gas to diffuse through the membrane without formingbubbles. Biofilm naturally grows on the outside wall of the membranefilaments. The H₂ electron donor meets the contaminant electron acceptorat that interface. Because of the counter-current transport of H₂ andthe oxidized contaminant in the biofilm, the H₂ utilization efficiencycan be nearly 100%, which enhances the economics and prevents forming anexplosive atmosphere above the water.

Hollow filaments may be made from a variety of gas-permeable,substantially liquid impermeable materials, including polyester,polyethylene, polypropylene, polyurethane, cellulose triacetate (CTA),Rayon® (a regenerated cellulosic fiber), and composites, thereof.

The hollow filaments may be individual filaments, filaments arranged intows or bundles, or filaments provided in a “tube sheet,” whereinmultiple substantially parallel filaments are imbedded in a sheet thatcan be folded or rolled up to provide MBfR filaments in layers of adesired density. The potted ends of the filaments may be machined toensure that the filaments are open and available to conduct gas. In someembodiments, the hollow filaments can be manipulated as a modular unit(i.e., “module”) for cleaning or replacement.

One class of compounds useful for the production of long hollowfilaments for use in continuous flow MBfR devices is the polyesters.Esters are a class of organic compounds traditionally formed by thecondensation of an alcohol and an organic acid. Where the acid is acarboxylic acid, the resulting ester has the structure R¹—C(═O)OR²,where R¹ and R² are independently H or myriad functional groups. Esterscan also be formed from phosphoric, sulfuric, nitric, boric, benzoic,and other acids. Cyclic esters are known as lactones.

Esters participate in hydrogen bonding as hydrogen-bond acceptors.However, esters do not function as hydrogen donors. This allows estersgroups to form hydrogen bonds with many other functional groups, whileprecluding hydrogen-bonding between esters groups. Esters are generallyhydrophobic, although the nature of the R¹ and R²-groups affects thecharacteristics of a particular ester.

Polyester is a polymer of one or more preselected ester monomers,typically produced by azeotrope esterification, alcoholictransesterification, acylation (i.e., the HCl method), the silyl orsilyl acetate method, or the ring-opening method, and variations,thereof, depending on the particular polyester. Polyester is widely usedin the manufacture of consumer products, and its mechanical propertiesare well known.

Polyesters include but are not limited to poly(ethylene terephthalate)(PET), poly(trimethylene terephthalate) (PTT), poly(butyleneterephthalate) (PBT), poly(ethylene naphthalate) (PEN),poly(cyclohexylene dimethylene terephthalate) (PCTA), polycarbonate(PC), poly(butylene naphthalate) (PBN), and poly(lactic acid) (PLA).Polyesters may be homopolymer or heteropolymers. As used herein,heteropolymers include copolymers. A common polyester co-polymers is1,4-cyclohexanedimethanol (CHDM). For example, PCTA is a copolymer ofthree monomers, which are terephthalic acid, isophthalic acid, and CHDM.While some industries use the terms “polyester” and “PET” almostinterchangeably, the term “polyester” refers to the entire class ofcompounds.

Many of the advantages of polyester are most apparent when filaments aretossed or woven into tows, ropes, fabrics, etc. For example, polyesteris widely used in the textile industry. The most widely used polyesteris PET (or PETE), which exists in amorphous (transparent) andsemi-crystalline (white or opaque) forms and is readily made intofilaments and sheets. PET and another polyester of a dihydric alcoholand terephthalic acid are commonly used to make rope.

In addition to being inexpensive to produce, polyesters are particularlystrong, resilient, resistant to abrasion, and resistant to stretchingand shrinking. Polyester textiles are wrinkle resistant, mildewresistant, fast drying, and retain heat-set pleats and creases.Polyester displays excellent resistance to oxidizing agents, cleaningsolvents, and surfactants. While resistant to sunlight, UV stabilizersare typically added for use outdoors or exposed to UV light.

Polyesters, like most thermoplastics, are recyclable and may be may bevirgin polyesters, recycled polyesters, post consumer polyesters,recycled monomers, or combinations and variations, thereof. Somepolyesters, including PET, offer the additional advantage of containingonly carbon, oxygen, and hydrogen (i.e., no sulfur, phosphorus,nitrogen, etc.), which makes them candidates for incineration.

Exemplary polyester hollow filaments are made of melt-spinnablepolyester, such as PET, that is melted and pressed through a hole of aspinneret, quenched in water or in an air stream, stretched in one ormore steps in combination with heating, and then wound onto on a spoolusing a winding machine. The hollow filaments are fine, effectively“endless” flexible hollow polyester tubes, which can be cut to anylength as needed. The filaments having an exterior surface that istypically exposed to the wastewater, and an interior surface forinteracting with sparged gas. The interior surface defines a hollowinterior space. Other polymer materials can be similarly spun to producelong hollow filaments.

The preferred diameter of the hollow filaments for use in the continuousflow MBfR depends on the particular embodiment. The hollow filaments maybe less than 500 μm in diameter, less than 300 μm in diameter, less than200 μm in diameter, or even less than 100 μm in diameter. The filamentsmay even be less than 50 μm, less than 20 μm, or even less that 10 μm indiameter. The hollow filaments may have a uniform diameter or beheterogenous with respect to diameter. Where the filaments are ofheterogenous diameter, the diameter may fall within a preselected range.The pore size of the filaments should such that the walls of thefilaments are gas permeable but substantially water impermeable. Anexemplary pore is about 0.1 to 0.15 μm.

The hollow filaments may be tossed into bundles to form multifilamentyarns, which are then assembled into modules for use in a bioreactor, tobe described. Filaments of less than 10 dtex (i.e., decitex=1 gram per10,000 meters) are preferred for yarns, while filaments of more than 100dtex are typically used as monofilaments. Intermediate filaments areused in either form. Both mono and multifilaments can be used as warp orweft in technical fabrics.

The diffusion of gas through a polymer membrane is generally describedby Fick's laws of diffusion. The solubility coefficient depends on theparticular polymer-gas combination and Henry's law. The permeation oflow molecular weight gases in rubbery polymers (below their glasstransition temperatures) at moderate pressures is Fickian and followsHenry's law for different sorption modes (i.e. absorption, theadsorption, plus trapping in microvoids, clustering, and aggregation).Klopffer, M. H. and Flaconneche, B., Oil & Gas Science andTechnology—Rev. IFP, 56, 2001, No. 3).

The burst pressure of a hollow filament can be calculated using Equation6:

P=T·(OD ² −ID ²)/(OD ² +ID ²)  (6)

where P is burst pressure, T is tenacity, and OD and ID are outside andinside diameter, respectively. OD and ID are preselected variables andtenacity is a constant associate with a particular polymer.

Preferred filament diameters for use as described are from about 50 μmto about 5,000 μm (OD), or even from about 0.10 mm to about 3,000 μm.One preferred diameter is about 300 μm. The optimal shape of hollowfilaments is round, although irregular shaper are expected to producesatisfactory results. Consistent density is preferred but not required.Preferred tenacity (T) values are from about 10 to about 80 cN/tex, oreven from about 20 to about 60 cN/tex.

Percent void volume (% V) may be calculated using Equation 7:

% V=T·(inside area)/(outside area)×100  (7)

An acceptable range for void volume is from about 1% to about 99%, whilea preferred range for some embodiments is from about 25% to about 50%.

B. Warp Fibers and Interleaf Materials

Hollow filaments may be combined with warp fibers, interleaf material,or both. Warp fibers are substantially inert, structural fibers orfilaments that are typically orientated perpendicular to the hollowfilaments. Interleaf material is generally in the form of a porous sheetused to separate layers of hollow filaments.

Warp fibers and interleaf materials can be made of polyester,polypropylene, polyethylene, polyurethane, cellulose triacetate, andcomposites, thereof. Preferred warp fiber have an outside diameter ofabout 100-500 μm, about 150-450 μm, or about 200-400 μm. In one example,the warp fiber is 150 denier textured polyester having an outsidediameter of about 300 μm and an inside diameter of about 150 μm. Otherdimensions and a range of from about 75 to about 300 denier texturepolyester should produce similar results.

Warp fibers should have some elasticity to allow the filaments to flexand expand, although the amount is not critical. The warp fibers may bespaced at intervals along the length of the hollow filaments. Thetension of the warp fibers may be sufficient to maintain the position ofthe groups of hollow filaments, minimizing the deflections and movementof the filaments under operating conditions; however, the filaments maybe able to flex and expand. The filaments may be arranged into groupsand then combined with warp fibers. Each group may include from 2 toabout 200 filaments.

Similarly, interleaf material may be made of an inert plastic materialsuch as of polyester, polypropylene, polyethylene, polyurethane,cellulose triacetate, and composites, thereof. Interleaf material shouldbe sufficiently porous to permit radial flow in an MBfR withoutsignificant restriction. Interleaf material may be made from wovenfibers, perforated sheets, or expanded materials. Exemplary interleafmaterial is an extruded polypropylene diamond net. A particular net hasa nominal hole size of 0.110 inches×0.110 inches, a thickness of 0.046inches, and a nominal open percentage of 66%.

While the present apparatus and methods have been described withreference to several embodiments, it will be appreciated that featuresand variations illustrated or described with respect to differentembodiments can be combined in a single embodiment. These and otherapplications and implementations will be apparent in view of thedisclosure. Such modifications, substitutions and alternatives can bemade without departing from the spirit and scope of the invention, whichshould be determined from the appended claims.

VI. EXAMPLES

The following Examples are provided to illustrate the present apparatusand methods and are in no way intended as limiting.

Example 1 Test Equipment

The specifications of the exemplary bench-scale MBfR reactor used in theexperiments described herein are provide in Table 5.

TABLE 5 MBfR device specifications Item Value Unit Active Length(vertical portion) 25 cm Shell Inside Diameter 0.6 cm Cross SectionalArea 0.28 cm² Active Volume (vertical portion) 7.07 cm³ Number of fibers32 Total Surface area of fibers 70.4 cm² Typical feed flow rate 0.2ml/min Typical detention time (empty-bed) 35 min Typical recycle flow150 ml/min Typical recycle ratio 750

A schematic of the exemplary bench-scale MBfR device and system is shownin FIG. 2. The MBfR system consisted of two glass tubes connected withNorprene tubing and plastic barbed fittings. One glass tube contained amain bundle of 32 hollow-filament membranes (Model MHF 200TL, MitsubishiRayon), each 25 cm long. The high recirculation rate of each reactor(i.e., 150 mL/min) promoted complete mixing and helped control biomassaccumulation on the filaments. A manifold peristaltic manifold pump wasused with PVC tubing to achieve a feed rate of about 0.2-0.3 mL/min. Thestandard hydrogen pressure for the reactors was 4-5 psi.

Example 2 Water Treatment Procedures

Water samples obtained from the Aerojet Facility were logged andrefrigerated until used as described herein. The MBfR device describedin Example 1 was operated in either a recycle (i.e., recirculating) modeor a feed mode. In the recycle mode, water was recirculated in the MBfRto allow the indigenous microorganisms to acclimate to the nutrientconditions and/or attach to the membrane filaments. The recirculationrate was about 200 ml/min but could be scaled appropriately to suitdifferent MBfR devices. Operation in the recirculating mode was stoppedwhen the nitrate concentration in the recirculating water becamenon-detectable (i.e., less than about 0.2 NO₃—N mg/L).

In the feed mode, fresh contaminated water was continuously fed into theMBfR, with a corresponding release of treated/decontaminated effluentwater. The feed rate was about 0.2 to about 0.3 mls/min with therecirculation rate being maintained at about 200 ml/min. These rates canbe adjusted to suit the particular apparatus used. Once the MBfR wasoperated in the feed mode, samples were collected periodically atpreselected times and send to Aerojet for analysis of perchlorate and/orTCE or analyzed for these or other contaminants at Applied.

Example 3 Analytical Testing

The pH of influent or effluent water was measured with an Oakton ModelPh Testr 3⁺. The nitrate concentration of influent or effluent water wasmeasured using a HACH Model# 820 and a Nitraver 5 test reagent (HachCompany, Loveland, Colo., USA). Perchlorate and TCE levels were measuredby Aerojet using standard procedures.

1. A method for reducing the concentration of oxidized contaminants present in ground water comprising: (a) providing an source of contaminated ground water comprising nitrate and perchorate to an MBfR device; (b) operating the MBfR device in a recycle mode using the contaminated ground water for a first period of time sufficient to form a biofilm in the MBfR device for performing denitrification in the influent water; and (c) operating the MBfR device in a feed mode using the contaminated water to produce denitrified effluent water; wherein the denitrified effluent water further comprises reduced levels of perchlorate compared to the influent water.
 2. The method of claim 1, wherein the influent water further comprises trichloroethylene (TCE), and the denitrified effluent water further comprises reduced levels of TCE compared to the influent water.
 3. The method of claim 2, wherein a chloride material balance calculation is performed to account for the chloride derived from the reduced TCE.
 4. The method of claim 1, wherein the influent water further comprises nitroso-dimethyl-amine (NDMA), and the denitrified effluent water further comprises reduced levels of NDMA compared to the influent water.
 5. The method of claim 1, wherein the levels of nitrate are substantially undetectable in recycle mode prior to switching to feed mode.
 6. The method of claim 1, further comprising: (d) operating the MBfR device in a recycle mode using influent water comprising at least a portion of effluent water from (c) for a second period of time sufficient to acclimate the biofilm to reduce perchlorate; and (e) operating the MBfR device in a feed mode using influent water comprising at least a portion of effluent water from (c) to reduce the levels of perchlorate in the influent water.
 7. The method of claim 6, wherein the influent water further comprises trichloroethylene (TCE), and the effluent water from (e) further comprises reduced levels of TCE compared to the influent water of (a).
 8. The method of claim 7, wherein a chloride material balance calculation is performed to account for the chloride derived from the reduced TCE.
 9. The method of claim 6, wherein the effluent water further comprises nitroso-dimethyl-amine (NDMA), and the effluent water from (e) further comprises reduced levels of NDMA compared to the influent water of (a).
 10. The method of claim 6, further comprising: (f) applying the effluent water from (e) to a second MBfR device having a biofilm acclimated to perchlorate reduction; and (g) operating the second MBfR device in a feed mode using as influent water the effluent water from (e) to produce effluent water from the second MBfR device having further reduced levels of perchlorate compared to the effluent water from the MBfR device of (a).
 11. The method of claim 10, wherein the levels of perchlorate after (g) are substantially undetectable.
 12. The method of claim 1, wherein denitrification and perchlorate reduction are performed by autotrophic bacteria using hydrogen gas as an electron donor.
 13. The method of claim 12, wherein the autotrophic bacteria are indigenous to the ground water.
 14. The method of claim 1, wherein the ability of the biofilm to perform denitrification in (b) is determined by comparing the concentration of nitrate in the recirculating water in the MBfR effluent water to the concentration of nitrate in the influent water.
 15. The method of claim 1, wherein the MBfR device comprises polyester hollow filaments for supporting the biofilm.
 16. A method for reducing the concentration of contaminants in ground water comprising: (a) providing a source of contaminated ground water comprising nitrate, perchorate, and trichloroethylene (TCE) and/or nitroso-dimethyl-amine (NDMA) to an MBfR device; (b) operating the MBfR device in a recycle mode using the contaminated ground water for a first period of time sufficient to form a biofilm in the MBfR device for performing denitrification in the influent water, wherein the ability of the biofilm to perform denitrification is determined by comparing the concentration of nitrate in the water in the recycle mode of the MBfR to the concentration of nitrate in the influent water; and (c) operating the MBfR device in a feed mode using the contaminated ground water to produce effluent water reduced in nitrate, perchorate, and TCE and/or NDMA; wherein the levels of nitrate, perchorate, and TCE and/or NDMA are reduced simultaneously.
 17. The method of claim 16, wherein the autotrophic bacteria are indigenous to the ground water.
 18. The method of claim 16, wherein a chloride material balance calculation is performed to account for the chloride derived from the reduced TCE.
 19. The method of claim 16, wherein the autotrophic denitrifying and perchlorate reducing bacteria are the same type of bacteria, which are acclimated to denitrifying and/or perchlorate reduction by operating the MBfR in a recycle mode using ground water from which nitrate and/or perchlorate is to be removed.
 20. The method of claim 16, wherein the autotrophic denitrifying and perchlorate reducing bacteria are different types of bacteria, which can be selected to form a biofilm for denitrifying and/or perchlorate reduction by operating the MBfR in a recycle mode using water from which nitrate and/or perchlorate is to be removed.
 21. Drinking water produced by simultaneously reducing nitrate and perchlorate contaminants in ground water using an MBfR device adapted to support a biofilm comprising autotrophic denitrifying and perchlorate reducing bacteria.
 22. The drinking water of claim 21, wherein simultaneously reducing nitrate and perchlorate contaminants in an MBfR device further includes simultaneously reducing trichloroethylene (TCE).
 23. The drinking water of claim 22, wherein a chloride material balance calculation is performed to account for the chloride derived from the reduced TCE.
 24. The drinking water of claim 21, wherein simultaneously reducing nitrate and perchlorate contaminants in an MBfR device further includes simultaneously reducing nitroso-dimethyl-amine (NDMA).
 25. The drinking water of claim 21, wherein simultaneously reducing nitrate and perchlorate contaminants is performed in a single MBfR device, or a plurality or MBfR devices in fluid communication with a common source of influent water.
 26. The drinking water of claim 25, wherein the MBfR or plurality of MBfR comprise polyester hollow filaments for supporting the biofilm. 